Such an electro-hydraulic brake system is disclosed by the unexamined German application DE 27 25 941, which is incorporated by reference. In the known brake system the hydraulic booster stage is connected to the inlet side of a pedal-operatable brake booster. A 3/2-way directional control valve, which is electrically controlled, serves as pressure regulating valve arrangement for regulating the hydraulic boost pressure. A feature of the known brake system that has been found to be less advantageous are the facts that in addition to the arrangement mentioned for generating an electrically controlled brake servo assistance, the pneumatic brake booster has to be used in order to afford brake servo assistance in the absence of electrical control. Two brake boosters, one electrical and one pneumatic, are used connected in series.
On the basis of the aforementioned use of a pedal-operatable brake booster and an electrically operatable brake booster, an object of the invention is to produce such a brake system having only one brake booster, which is both pedal-operatable and electrically operatable.